Move the *PassPrinter into their own module.

These are self-contained in functionality so it makes sense to separate them,
as opt.cpp has grown quite big already.

Following Eric's suggestions, if this code is ever deemed useful outside of
tools/opt, it will make sense to move it to one of the LLVM libraries like IR.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201116 91177308-0d34-0410-b5e6-96231b3b80d8